1. Field of the Invention
The present invention relates to the structure of a three link vehicle suspension system including a pair of radius arms and a track bar.
2. Background Art
Vehicle suspension systems connect an axle to a frame of a vehicle. Suspension system components typically include shock absorbers, springs, torsion bars, and other components. Vehicle suspensions are dynamic systems that move in response to braking, turning, acceleration and road induced impacts. The vehicle must be designed to allow for substantial movement of suspension system components relative to each other and to the other vehicle components.
Four and five link suspension systems have been developed that offer some advantages in regard to vehicle design. However, these systems have pairs of upper and lower arms that increase the cost and part count of the suspension systems. In addition, four and five link systems generally require a greater number of expensive bushings.
One example of a heavy duty suspension system is a three link suspension system that may include two radius arms and a track bar. The radius arms connect through rubber bushings to the frame and normally extend below the axle. Radius arms generally connect to axle mounting structures that are located fore and aft of the axle. The track bar, also known as a Panhard rod, is a lateral restraint which may be replaced with a Watt's linkage that laterally connects to the axle and the frame through rubber bushings or an equivalent joint such as a spherical joint. The track bar and steering links may be located on the opposite side of the axle from the side on which the radius arms are connected to the frame. Any portion of the radius arms that extend beyond the axle to the opposite side may complicate suspension system design and create interference with the steering linkage.
Radius arms must be strong and durable to withstand impacts and stresses encountered in normal and extreme driving conditions. Suspension systems must provide acceptable ride quality and minimize harshness. Rubber bushings are used to absorb vibration and soften the ride of a vehicle. Bushings may be selected to tune roll stiffness, caster stiffness, caster change, steering, and tracking performance characteristics.
Normally, the longer the radius arm, the lower the amount of brake anti-dive. Longer radius arms also tend to reduce the caster angle sensitivity relative to suspension deflection and ride height.
The roll stiffness of a front suspension linkage may be impacted by bushing radial stiffness, bushing separation distance, axle tube torsional stiffness, radius arm bending stiffness, radius arm lateral separation and the radius arm length. While all of the above factors may impact roll stiffness, generally the longer the radius arm, the lower the roll stiffness and the stiffer bushings must be to compensate.
Bushings used in suspension systems may exhibit different loading characteristics. Bushings may exhibit conical loading, particularly if the bushings are installed fore-and-aft of the axle as in typical suspension system designs. Radial loading of bushings is generally preferred because it is more predictable and maximizes bushing performance characteristics.
The above problems and challenges are addressed by applicants' invention as summarized below.